June : 2016 (CBCS) Negative terminal for forward bias. Positive terminal for forward bias. Cathode ( n-type)

Transcription

1 s Year : Commo o all raches Jue : 6 (CCS) Noe : Max. marks : 6 (i) (ii) (iii) (iv) emp ay five quesios ou of seve quesios. ll quesios carry equal marks. Draw he ea diagram, wheever ecessary. ssume daa, wherever ecessary. Q. (a) Defie diode. Describe heory of diode operaio. Wha is he applicaio of i? Diode : p jucio forms a popular semicoducor device called p jucio diode. I has wo ermials called elecrodes, oe elecrode each from p regio ad regio hece called diode (Di + elecrode). Posiive ermial for forward bias I F Negaive ermial for forward bias rrowhead idicaes coveioal curre direcio I he symbol of a diode, a arrowhead idicaes he coveioal curre direcio whe i is forward biased. diode allows curre o flow i oly oe direcio. Operaio : Forward bias :. p jucio is forward bias whe a volage is applied posiive o he p side ad egaive o he side.. Whe a diode is coeced i a forward bias, he egaive ermial of he baery pushes he free elecros i regio owards he jucio. Similarly he holes from p regio are repelled by he posiive ermial of he baery ad move owards he jucio. 3. forward biased jucio has a arrow depleio regio. 4. The forward bias applied volage V a origial value V o V V. 5. The elecric field reduces. J 6. The immobile ios i depleio regio reduces. + J a ode ( p-ype) Cahode ( -ype), reduces he barrier poeial across he jucio from is 7. majoriy charge carrier curre flows across a forward bias jucio. V J V a p-regio Depleio regio -regio + V a

2 s Year : Commo o all raches Reverse bias :. p jucio is reverse bias whe a volage is applied posiive o he side ad egaive o he p side. p +. Whe a diode is coeced i a reverse bias, he egaive ermial of he baery aracs he holes i p regio away from he jucio. Similarly he elecros from regio are araced by he posiive ermial of he baery ad move away from he jucio. 3. reverse biased jucio has a wide depleio regio. 4. The reverse bias applied volage V a origial value V o V V. 5. The elecric field icreases. J 6. The immobile ios i depleio regio icreases. J a, icreases he barrier poeial across he jucio from is 7. very small mioriy charge carrier curre flows across a reverse bias jucio. p-regio V J V a V a Depleio regio -regio + pplicaio :. Recifiers which are furher classified as half wave, full wave ad bridge recifiers.. Clipper circuis o remove uwaed porios of waveform. 3. Clamper circuis o add DC level o waveform. 4. Volage mulipliers such as volage doubler, volage ripler ec. 5. Various elecroic ad operaioal amplifier circuis such as volage o curre coverers, log ad ailog amplifiers, precisio recifiers, proecio circuis ec. Q. (b) Wha are he ypes of diode? Lis hem ad draw heir symbol. Types of diode ad heir symbol : V a Name Symbol Geeral purpose diode Zeer diode Schoky diode Varacor/varicap diode

3 3 s Year : Commo o all raches Tuel diode Ligh emiig diode (LED) Phoodiode Pi diode Q. (a) Deermie he decimal umbers represeed by followig biary umbers : (i) (ii) (iii) (iv) (i) N N N (ii) N N 384 N (iii) () () N N 55 () (55) (iv) N N Q. (b) Perform he followig : (i) ddiio (?) (ii) Subracio (?) (i) ddiio (?)

4 4 s Year : Commo o all raches (ii) Subracio (?) Q.3 (a) Describe he OR, ND, NND gae wih he help of ruh able. ND gae : logic circui whose oupu is HIGH oly whe all ipus are HIGH. Symbol of ND gae : Truh able of ND gae : Ipus Oupu Y Y Oupu is whe all ipus are OR gae : logic circui whose oupu is HIGH whe aleas oe ipu is HIGH. Symbol of OR gae : Truh able of OR gae : Ipus Oupu Y Y Oupu is whe all ipus are NND gae : logic circui whose oupu is LOW whe all ipus are HIGH. Symbol of ipu NND gae : Y Truh able : Ipus Oupu Y Oupu is whe all ipus are

5 5 s Year : Commo o all raches Q.3 (b) Give he logical equaio Y ( C)( C). Desig a circui usig gaes o realize his fucio. Give oolea fucio is, Y ( C)( C) Y CCC C Y C C [ND law : X X X ad X X ] Y C Y C ( ) C ( ) C ( C) [OR law : X X ] Y C C C C C C Y C C C C Y C ( ) C ( ) [OR law : X X ] Logic diagram : Y C C C C C C Q.4 (a) Defie aalog ad digial commuicaios. Draw he basic block diagram of rasmier ad receivers. alog commuicaio : alog commuicaio is ha ypes of commuicaio i which he rasmied message or iformaio sigal is aalog i aure. This meas ha i aalog commuicaio he modulaig sigal i.e. base bad sigal is a aalog sigal. This aalog message sigal may be obaied from sources such as speech, video shooig ec. Digial commuicaio : I digial commuicaio, he message sigal o be rasmied is digial i aure. This meas ha digial commuicaio ivolves he rasmissio of iformaio i digial form. The immuiy o chael oise ad exeral ierferece is beer ha aalog commuicaio. lock diagram of rasmier ad receiver :. Radio rasmier : radio rasmier cosiss of several elemes ha work ogeher o geerae radio waves ha coai useful iformaio such as audio, video, or digial daa. (i) Power supply : I provides he ecessary elecrical power o operae he rasmier. (ii) Oscillaor : I creaes aleraig curre a he frequecy o which he rasmier will rasmi. The oscillaor usually geeraes a sie wave, which is referred o as a carrier wave. (iii) Modulaor : I adds useful iformaio o he carrier wave. There are wo mai ways o add his iformaio. The firs, called ampliude modulaio or M, makes sligh icreases or decreases o he ampliude of he carrier wave. The secod, called frequecy modulaio or FM, makes sligh icreases or decreases he frequecy of he carrier wave. (iv) mplifier : I amplifies he modulaed carrier wave o icrease is power. The more powerful he amplifier, he more powerful he broadcas. (v) ea : I covers he amplified sigal o radio waves.

6 6 s Year : Commo o all raches ea Power supply Oscillaor Modulaor mplifier udio or video iformaio Fig. lock diagram of rasmier. Radio receiver : radio receiver is he opposie of a radio rasmier. I uses a aea o capure radio waves, processes hose waves o exrac oly hose waves ha are vibraig a he desired frequecy, exracs he audio sigals ha were added o hose waves, amplifies he sigals. (i) ea : I capures he radio waves. Typically, he aea is simply a legh of wire. Whe his wire is exposed o radio waves, he waves iduce a very small aleraig curre i he aea. (ii) RF amplifier : sesiive amplifier ha amplifies he very weak radio frequecy (RF) sigal from he aea so ha he sigal ca be processed by he uer. (iii) Tuer : circui ha ca exrac sigals of a paricular frequecy from a mix of sigals of differe frequecies. O is ow, he aea capures radio waves of all frequecies ad seds hem o he RF amplifier, which duifully amplifies hem all. (iv) Deecor : I is resposible for separaig he audio iformaio from he carrier wave. For M sigals, his ca be doe wih a diode ha jus recifies he aleraig curre sigal. (v) udio amplifier : This compoeʹs ask is o amplify he weak sigal ha comes from he deecor so ha i ca be heard. This ca be doe usig a simple rasisor amplifier circui. ea RF amplifier Tuer Deecor Fig. lock diagram of receiver udio amplifier Q.4 (b) Draw he various RF bads of IEEE specrum ad wrie heir applicaios. I wireless commuicaio, elecromageic waves are used as a media for rasfer of iformaio. Thus i such a commuicaio, he iformaio sigal is covered io he elecromageic sigal before rasmissio. The elecromageic (EM) waves cosis of boh elecric ad mageic fields ad hey ca ravel a log disace hrough space. The rage of all possible frequecies of EM waves is called he elecromageic specrum, show i he figure below. I exeds from he frequecies used for moder radio (a he log wavelegh ed) o gamma radiaio (a he shor wavelegh ed). I he mid rage icludes mos commoly used radio frequecies for wo way commuicaios, elevisio ad oher applicaios.

7 7 s Year : Commo o all raches m m m m m m m m 4 3 Wavelegh m m m 3 m 4 m 5.4 x m(viole) 6.7 x m(red) 6 ELF VF VLF LF MF HF VHF UHF SHF EHF Millimeer waves Ifrared Visible ligh Ulraviole X-rays Gamma rays Cosmic rays 3Hz 3Hz 3kHz Fig. Elecromageic specrum The able below shows he radio frequecy specrum ad is applicaio accordig o various frequecy bads. Frequecy bad Frequecy Wavelegh pplicaios Exremely low frequecy (ELF) 3 3 Hz 4 3 km km Commuicaio wih submaries 3 Voice frequecy (VF) 3 3 Hz km km udio applicaio Very low frequecy (VLF) 3 3 khz km km Submarie commuicaio, avalache beacos, wireless hear rae moiors, geophysics Low frequecy (LF) 3 3 khz km km Navigaio, ime sigals, M log wave broadcasig Medium frequecy (MF) 3 3 khz km m M (Medium wave) broadcass High frequecy (HF) 3 3 MHz m m Shorwave broadcass, amaeur radio ad over he horizo aviaio commuicaios Very high frequecy (VHF) Ulra high frequecy (UHF) Super high frequecy (SHF) Exremely high frequecy (EHF) 3kHz 3 khz 3MHz 3MHz 3 MHz 3 3 MHz m m FM, elevisio broadcass ad lie of sigh groud o aircraf ad aircraf o aircraf commuicaios 3 3 MHz 3GHz 3GHz Frequecy 3 GHz m mm Televisio broadcass, mobile phoes, wireless LN, blueooh ad wo way radio such as FRS ad GMRS radios 3 3 GHz mm mm Microwave device, wireless LN, mos moder radars 3 3 GHz mm mm Radio asroomy, high speed microwave radio relay

8 8 s Year : Commo o all raches Q.5 (a) How NOT operaio ca be performed usig rasisor? Describe. Whe ipu X, he base of he rasisor is low () ad herefore rasisor operaes i cu off regio IC. Hece o volage drop across R C ad oupu Y is V CC (HIGH). Whe ipu X, he base of he rasisor is high () ad herefore rasisor operaes i sauraio regio. I he sauraio regio V. V. Hece oupu volage. V, i.e. CE logic (Low). Thus for he circui show i figure oupu is compleme of ipu ad we ca say ha i represes NOT gae. Q.5 (b) Describe various oolea ideiies. Draw he ND circui usig diode logics. Laws of oolea algebra are used for simplifyig a complex oolea expressio. The differe oolea laws are discussed as follows :. OR law : The followig heorems impleme he OR law : (i) Ou of wo variables o be ORed, if ay oe variable is low (), he he oupu value is he oher variable i.e. (ii) Ou of wo variables o be ORed, if ay oe variable is high (), he he oupu value is high i.e. (iii) If boh variables o be ORed have he same value, he he oupu value is of oe ipu variable i.e. (iv) Ou of wo variables o be ORed, if ay oe variable is he compleme of he oher, he he oupu value is high i.e.. ND law : The followig heorems impleme he ND law : (i) Ou of wo variables o be NDded, if ay oe variable is low (), he he oupu value is zero i.e. (ii) Ou of wo variables o be NDed, if ay oe variable is high (), he he oupu value is oher variable i.e. (iii) If boh variables o be NDed have he same value, he he oupu value is also he same of oe of he variable i.e. (iv) Ou of wo variables o be NDed, if ay oe variable is he compleme of he oher, he he oupu value is zero i.e. 3. Commuaive law : I saes ha chagig he sequece of he variables o perform logic operaio does o chage he oupu, which meas ha chage of variable sequece is allowed i.e. X V CC + R C V CE Fig. NOT gae usig rasisor Y

9 9 s Year : Commo o all raches 4. ssociaive law : I saes ha chagig he order of logic operaios does o chage he oupu, which meas ha chagig he order of logic operaios is allowed i.e. ( C) ( ) C ( C) ( ) C 5. Disribuive law : I saes ha NDig he resul of several ORed variables wih a sigle variable is he same as NDig resul wih a idividual variable wih each of he muliple variables, ad is produc is a ORed variable i.e. ( C) C ( C) ( ) ( C) ( ) ( ) ( ) ( ) ( ) 6. Complemeaio law : I saes ha he compleme of is, of is, ad of is i.e. 7. bsorpio law : I saes he followig properies : ( ) 8. Idempoecy law : I saes he followig properies : 9. Iversio law : I saes ha if a variable is subjeced o a double iversio ha i will resul i he origial variable iself i.e. ND gae circui usig diode : +5V R + 5V= V = C D D Y Fig. Diode ND gae circui usig posiive logic D 3 I Fig. for posiive logic, if ay of he hree ipus is a V (logic ), he correspodig diode becomes forward biased or coducig showig zero resisace ad hece he volage a Y becomes zero. If all he ipus, ad C are a +5 V (logic ), he diodes are i reversed bias, hece o diode coducs ad he volage a Y will be +V (logic ) This is described wih he help of he ruh able show i Fig..

10 s Year : Commo o all raches C Y Fig. Truh able for ND gae Q.6 (a) Compare half wave recifier wih full wave recifier wih ea skech. S. No. Pariculars HWR FWR. Number of diodes. DC curre I m / Im / 3. DC volage Vm / Vm / 4. RMS curre I m / I / 5. Ripple facor Maximum efficiecy 4.6% 8.% 7. TUF PIV Vm V m 9. Oupu frequecy f f. Form facor.57.. Peak facor.44 m. Figure D R L v + M G V m D i C Ipu N V m D i + R L Q.6 (b) Wha is sigal? Defie. mpliude is impora variable parameers of sigal. Wha kid of operaios ca be performed wih ampliude? Describe. Sigal is a fucio which coveys some iformaio. sigal is defied as a physical quaiy ha varies wih ime, space or ay oher idepede variable. Example : (i) Elecric volage or curre, such as radio sigal, TV sigal, elephoe sigal, compuer sigal ec. (i) Pressure sigal, soud sigal ec. are o elecric sigals. Mahemaically, a sigal is represeed as a fucio of a idepede variable. Usually, represe ime. Thus, a sigal is deoed by x(). Classificaio of sigals :. Coiuous ad discree ime sigals. alog ad digial sigals 3. Deermiisic ad radom sigals 4. Eve ad odd sigals 5. Periodic ad o periodic sigals 6. Eergy ad power sigals

11 s Year : Commo o all raches mpliude scalig : Cosider a sigal x() is provided ad we have o scale or muliply i by facor, where ca be ay value., he ampliude compress by a facor., he he ampliude is sreched by facor. 4 x () x () x () / mpliude iversio : x () x () Example : Cosider a sigal x(). Time For x () mpliude x () x () x () x () x() For x(), muliply ampliude wih. Q.7 (a) Describe differe aalog ad digial sigal i deail. alog sigal : (i) Ui sep sigal : for Ui sep sigal is defied as, u ().5 for for The ui sep sigal is discoiuous a ad a is value is udefied. So, u( ) u( ) u() The ui sep fucio is also kow as Heaviside ui fucio. u () (ii) Ui ramp sigal : Ui ramp sigal is defied as, for r () for

12 s Year : Commo o all raches 3 r () (iii) Ui impulse sigal : The impulse sigal is a sigal wih ifiie magiude ad zero duraio, bu wih ui area. The ui impulse fucio is also kow as he Dirac dela fucio. a Mahemaically, δ( ) ad () d a (iv) Expoeial sigal : Expoeial sigals are of wo ypes : (a) Real expoeial sigal : x() e If, he x() is a growig expoeial, ad if, he x() is a decayig expoeial. x () e ; 3 x () e ; () j (b) Complex expoeial sigal : x() e cos jsi The sigal x() is kow as complex expoeial sigal whose real par is cos ad imagiary par is si. I is periodic wih ime period T π / ω. The geeral complex expoeial sigal is, x e e e j s ( j) () (cos si ) where real par e cos ad imagiary par e si The real par of complex frequecy variable is called aeuaio or growh cosa. I deoes by how much amou ampliude of he sigal is icreased or decreased. The imagiary par of a complex frequecy variable is called agular frequecy wih a usual meaig. Wih ad, x() i.e. cosa ampliude sigal. Wih ad s ad, x() e i.e. expoeially growig sigal. Wih ad s ad, x() e i.e. expoeially decayig sigal. j Wih s j, x () e, i.e. purely siusoidal sigal wih susaied oscillaios. Wih s j ad, we ge siusoidal sigal wih decayig oscillaios. Wih s j ad, we ge siusoidal sigal wih growig oscillaios.

13 3 s Year : Commo o all raches e si ; e si ; Digial sigal : (i) Ui sep sequece : Ui sep sequece is mahemaically defied as, for u ( ) for The value of u ( ) a is defied ad equals uiy. (ii) Ui ramp sequece : Ui ramp sequece is defied as, for r ( ) for r ( ) 3 (iii) Ui sample sequece : Ui sample sequece is defied as, a ( ) a 3 ( ) (iv) Expoeial sequece : Expoeial sequeces are of wo ypes : (a) Real expoeial sequece : x( ) e If, he x( ) is a growig expoeial. If, he x( ) is a decayig expoeial. x ( ) e ; x ( ) e ;

14 4 s Year : Commo o all raches j (b) Complex expoeial sequece : x( ) e cos jsi The sigal x( ) is kow as complex expoeial sigal whose real par is cos ad imagiary par is si. The geeral complex expoeial sigal is, x e e e j s ( j) ( ) (cos si ) whose real par e cos ad imagiary par e si are expoeially icreasig if ad expoeially decreasig if. e si ; e si ; (v) Recagular pulse sequece : Le L be a posiive odd ieger. impora example of a discree ime sigal is he discree ime recagular pulse fucio rec[ ] of legh L defied by,, ( L)/,...,,,,...( L)/ rec[ ], all oher The discree ime recagular pulse is show i figure. rec [ ] ( L ) 3 3 L Q.8 (b) How aalog sigal ca be covered io a digial oe? Describe. alog sigal ca be covered io digial sigal by followig procedure as show i figure below. Sampler Quaizer Ecoder m () m s () m q () T s T s T s 3T s Fig. lock diagram of aalog o digial coverer Sampler : I covers coiuous ampliude coiuous ime sigal io coiuous ampliude discree ime sigal.

15 s Year : Commo o all raches 5 Quaizer : I covers coiuous ampliude discree ime sigal io discree ampliude discree ime sigal. I approximaes each sample io is eares sadard volage level called quaizaio level. I is a process of roudig off he sigal. Ecoder : ecoder covers each quaized sample io disic code word. Thus a he oupu of he ecoder we ge digial code words.